The Phoenix mission was the first chosen for NASA's Scout program, an initiative for smaller, lower-cost, competed spacecraft. Named for the resilient mythological bird, Phoenix used a lander that was intended for use by 2001's Mars Surveyor lander prior to its cancellation. It also carried a complex suite of instruments that were improved variations of those that flew on the lost Mars Polar Lander.

In the continuing pursuit of water on Mars, the polar regions are a good place to probe, as water ice is found there. Phoenix landed farther north than any previous mission, at a latitude equivalent to that of northern Alaska. During the course of its three-month mission, Phoenix dug into an ice-rich layer near the surface. It checked samples of soil and ice for evidence about whether the site was ever hospitable to life.

To analyze soil samples collected by its robotic arm, Phoenix carried tiny ovens and a portable laboratory. Selected samples were heated to release volatiles that were examined for their chemical composition and other characteristics.

Phoenix's stereo camera, located on its 2-meter (6.6-foot) mast, used two "eyes" to reveal a high-resolution perspective of the landing site's geology. It also provided range maps for the team's use in choosing where to dig. Multi-spectral capability enabled the identification of local minerals.

To update our understanding of Martian atmospheric processes, Phoenix also scanned the atmosphere up to 20 kilometers (12.4 miles) in altitude, obtaining data about the formation, duration and movement of clouds, fog, and dust plumes. It also carried temperature and pressure sensors.